Fabrication of ultrasmall Nb-AlOx-Nb Josephson tunnel junctions

Abstract
We describe a fabrication process to make Nb‐AlOx‐Nb edge junctions with areas as small as 0.0022 μm2 and with current densities from 10 to 24 000 A/cm2. The junction conductance was low for voltages below the superconducting energy gap which indicates good quality tunnel barriers. Coulomb gap measurements obtained when the junctions were in the normal state were used to find the junction capacitance. Junction capacitance as small as 0.18 fF has been measured.